In electrophotographic fuser systems, fuser roller overcoats are made with layers of polydimethylsiloxane (PDMS) elastomers, fluorocarbon resins, and fluorocarbon elastomers. PDMS elastomers have low surface energy and relatively low mechanical strength, but is adequately flexible and elastic and can produce high quality fused images. After a period of use, however, the self-release property of the roller degrades and offset begins to occur. Application of a PDMS oil during use enhances the release property of the fuser roller surface but shortens roller life due to oil swelling. Fluorocarbon resins like polytetrafluoroethylene (PTFE) have good release property but less flexibility and elasticity than PDMS elastomers. Fluorocarbon elastomers, such as Viton.TM. and Fluorel.TM., are tough, flexible, resistant to high temperatures, durable and do not swell, but they have relatively high surface energy and poor thermal conductivity.
Particulate inorganic fillers have been added to fluorocarbon elastomers and silicone elastomers to increase mechanical strength and thermal conductivity. High thermal conductivity is an advantage because heat needs to be efficiently and quickly transmitted to the toner from the outer surface of the fuser roller to fuse the toners and yield the desired toner images. However, incorporation of inorganic fillers to improve thermal conductivity has a major drawback: it increases the surface energy of fuser roller surface and also increases the interaction of the filler with the toner and receiver. After a period of use, the toner release properties of the roller degrade and toner offset begins to occur due to roller wear and weak interaction between the filler and the polymer matrix. It would be desirable to provide a fuser member having a fluorocarbon elastomer overcoat layer containing thermally conductive inorganic fillers, but which still has good toner release property. In addition, the outer surface of the fuser member should be compatible with the functionalized polymeric release agent employed during the fixing process.
Fuser members of fluorocarbon elastomer containing inorganic fillers are disclosed, for example, in U.S. Pat. No. 5,595,823 to Chen et al. Which describes fuser rollers having a surface layer comprising fluorocarbon elastomer and aluminum oxide fillers. These fillers are not treated and are prone to high reactivity with the toner and charge control agents and this, too, is undesirable.
U.S. Pat. No. 5,017,432 to Eddy et al. describes a fluorocarbon elastomer fuser member which contains cupric oxide to interact with the polymeric release agent and provide an interfacial barrier layer. U.S. Pat. No. 5,464,698 to Chen et al. describes fuser rollers having a surface layer comprising fluorocarbon elastomer and tin oxide fillers. The fillers provide active sites for reacting the mercapto-functional polydimethylsiloxane.
Fuser members of condensation-crosslinked PDMS elastomers filled with metal oxides are disclosed, for example, in U.S. Pat. No. 5,401,570 to Heeks et al. This patent describes a silicone rubber fuser member containing aluminum oxide fillers which react with a silicone hydride release oil.
U.S. Pat. No. 5,480,724 to Fitzgerald et al. discloses tin oxide fillers which decrease fatigue and creep (or compression) of the PDMS rubber during continuous high temperature and high stress (i.e. pressure) conditions.
Some metal oxide filled condensation-cured PDMS elastomers are also disclosed in U.S. Pat. No. 5,269,740 (cupric oxide filler), U.S. Pat. No. 5,292,606 (zinc oxide filler), U.S. Pat. No. 5,292,562 (chromium oxide filler), and U.S. Pat. No. 5,336,596 (nickel oxide filler). All provide good results.
Fillers useful in one elastomer material may not be useful in a different elastomer due to chemical or other interactions that may differ substantially between material types. Different metal oxides also may behave differently and be unsuitable for use in a fuser member. U.S. Pat. No. 4,264,181 to Lentz et al. includes lead oxide as a suitable filler in various fluorocarbon elastomers (Viton E430, VitonE60C, Viton GH), yet U.S. Pat. No. 5,017,432 teaches that lead oxide is undesirable on the basis that it produces an unacceptable fuser member in similar fluorocarbon elastomers (Viton GF). U.S. Pat. No. 4,515,884 to Field et al. discloses a fuser member which utilizes metal oxide filled polydimethylsiloxane. The metal oxides are iron and tabular alumina, while calcined alumina is described as being unsuitable for use. U.S. Pat. No. 4,562,335 discloses a silicon carbide filled condensation-cured PDMS elastomer providing good release. U.S. Pat. No. 4,763,158 describes boron nitride as a useful filler in polydimethylsiloxane elastomers; however results described therein indicate that in fluorocarbon elastomers it demonstrates poor release performance and is unsuitable for use.
This application is related to the following commonly owned US applications: U.S. Ser. No. 08/962,129, U.S. Pat. No. 6,114,041, of Tan, Chen, Binga and Wilkins, titled FUSER MEMBER WITH SURFACE TREATED Al.sub.2 O.sub.3 AND FUNCTIONALIZED RELEASE FLUIDS; U.S. Ser. No. 08/961,838, U.S. Pat. No. 5,998,033, of Tan, Chen, Binga and Wilkins, titled FUSER MEMBER WITH CHEMICALLY MODIFIED ELASTOMER/FILLERS AND FUNCTIONALIZED RELEASE FLUIDS; and U.S. Ser. No. 08/962,108, U.S. Pat. No. 5,935,712, of Tan, Chen, Binga and Wilkins, titled FUSER MEMBER CONTAINING SURFACE TREATED TIN OXIDE.
Unfortunately, as fuser rollers wear, the fillers that are exposed react not only with the functionalized polymeric release agent, but also with the toner, paper substrate and charge control agent. Such reactions build up debris on the surface of the fuser roller, causing deterioration of toner release and great reduction in the life of the fuser roller. Thus, there remains a need for fuser members whose fillers have a low propensity to react with toners or are made to enhance the interaction between the elastomer and filler and also between the polymeric release agent and filler.